Method of laser processing of a metallic material with optical axis position control of the laser relative to an assist gas flow, and a machine and computer program for the implementation of said method

ABSTRACT

A method of laser processing of a metallic material is described, by means of a focused laser beam having a predetermined transverse power distribution on at least one working plane of the metallic material, comprising the steps of:
         providing a laser beam emitting source;   leading the laser beam along a beam transport optical path to a working head arranged in proximity to the material;   collimating the laser beam along an optical axis of propagation incident on the material;   focusing the collimated laser beam in an area of a working plane of the material; and   conducting the focused laser beam along a working path on the metallic material comprising a succession of working areas,   wherein the laser beam is shaped:   by reflecting the collimated beam by means of a deformable, controlled surface reflecting element having a plurality of independently movable reflection areas, and   by controlling the arrangement of the reflection areas to establish a predetermined transverse power distribution of the beam on at least one working plane of the metallic material as a function of the area of the current working plane and/or of the current direction of the working path on the metallic material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Italian Patent Application No.102016000070259 filed on Jul. 6, 2016, the entire contents of which ishereby incorporated in its entirety by reference.

FIELD OF THE INVENTION

The present invention relates to the laser processing of a metallicmaterial, more specifically, a laser processing method for cutting,drilling or welding of said material.

According to other aspects, the present invention relates to a machinefor laser processing of a metallic material arranged to implement thelaser processing method, and a computer program comprising one or morecode modules for implementing the aforementioned method when the programis executed by electronic processing means.

BACKGROUND OF THE INVENTION

In the following description and the claims, the term “metallicmaterial” is used to define any metallic workpiece such as a sheet orelongated profile having indifferently a closed cross-section—forexample a hollow circular, rectangular or square form—or an openone—e.g. a flat section or a section in the form of an L, C, U, etc.

In industrial metal processing methods, and in particular those ofmetallic sheets and profiles, the laser is used as a thermal tool for awide variety of applications that depend on the interaction parametersof the laser beam with the material being processed, specifically on theenergy density per incidence volume of the laser beam on the materialand on the interaction time interval.

For example, by directing a low energy density (on the order of tens ofW per mm² of surface) for a prolonged time (on the order of seconds), ahardening process is achieved, while directing a high energy density (onthe order of tens of MW per mm² of surface) for a time on the order offemtoseconds or picoseconds, a photo-ablation process is achieved. Inthe intermediate range of increasing energy density and decreasingworking time, the control of these parameters enables welding, cutting,drilling, engraving and marking processes to be carried out.

In many processes, including drilling and cutting processes, an assistgas flow must be provided to the working region wherein the interactionbetween the laser beam and the material occurs which has the mechanicalfunctions of propulsion of the molten material, or the chemicalfunctions of assisting the combustion, or even the technologicalfunctions of shielding from the environment surrounding the workingregion.

In the field of laser processing of metallic materials, laser cutting,drilling and welding are processing operations that may be carried outby the same machine, which is adapted to generate a high-powered focusedlaser beam having a predetermined transverse power distribution on atleast one working plane of the metallic material, typically a laser beamwith a power density ranging from 1 to 10000 kW/mm², and to govern thebeam direction and position of incidence along the material. Thedifference between the different types of processing that may beperformed on a material is substantially ascribable to the power of thelaser beam used and the time of interaction between the laser beam andthe material subject to processing.

Laser processing machines according to the prior art are shown in FIGS.1 and 2.

FIG. 1 schematically shows an industrial processing machine with a CO₂laser with an optical path of the laser beam in the air, which comprisesan emitting source 10, such as a CO₂ laser generator device, capable ofemitting a single-mode or multi-mode laser beam B and a plurality ofreflective mirrors 12 a, 12 b, and 12 c adapted to conduct the laserbeam emitted from the emitting source along a beam transport opticalpath towards a working head, indicated collectively at 14, arranged inproximity of a material WP. The working head 14 comprises an opticalfocusing system 16 of the laser beam, generally consisting of a focusinglens, adapted to focus the laser beam along an optical axis ofpropagation incident on the metallic material. A nozzle 18 is arrangeddownstream of the focusing lens and is crossed by the laser beamdirected towards an area of a working plane of the material. The nozzleis adapted to direct a beam of an assist gas injected by a correspondingsystem not shown toward the working area on the material. The assist gasis used to control the execution of a working process as well as thequality of the processing obtainable. For example, the assist gas maycomprise oxygen, which favors an exothermic reaction with the metal,allowing the cutting speeds to be increased, or an inert gas such asnitrogen which does not contribute to the fusion of the material butprotects the material from unwanted oxidation at the edges of theworking profile, protects the working head from any splashes of moltenmaterial and may also be used to cool the sides of the groove producedon the material, confining the expansion of the thermally altered area.

FIG. 2 shows schematically an industrial processing machine with thelaser beam channeled through fiber optics. It comprises an emittingsource 10, such as a laser generating device capable of feeding a laserbeam into a transport fiber, for example a laser fiber doped withytterbium, or a direct diode laser, adapted to emit a single-mode ormulti-mode laser beam, and a fiber optic cable 12 d adapted to conductthe laser beam emitted from the emitting source to the working head 14arranged in proximity to the material M. At the working head, the laserbeam emerging from the fiber with its divergence controlled iscollimated by a collimating dioptric system 20 and reflected by acatoptric system 22 before being focused through an optical focusingsystem 16, generally consisting of a focusing lens, along an opticalaxis of propagation incident on the WP material passing through theemitting nozzle 18.

FIG. 3 illustrates an exemplary working head 14 according to the priorart. At 30 a tubular channel is represented having cylindrical orconical sections within which the laser beam is transmitted, indicatedat B. The laser beam B generated by the emitting source 10 andtransported to the working head by means of an optical path in air withmultiple reflections or in fiber optics collimates on a reflectivedeflector element 32 that deflects its optical propagation axis in adirection of incidence on the material being processed. The opticalfocusing system 16 is intermediate between the reflective deflectorelement 32 and a protective slide 34 arranged downstream, adapted toshield the focusing system from any splashes of molten material, andcomprises a lens holder unit 36 to which are coupled mechanicaladjustment mechanisms 38 for calibrating the positioning of the lenstransversely to the direction of propagation of the beam (X-Y axes) andin the direction of propagation of the beam (Z axis).

The optical processing to which the laser beam is subjected in theworking head is diagrammed in FIGS. 4 and 5.

The laser beam B originating from an emitting source S through anoptical transport path in the free space or in the fiber reaches theworking head with a predetermined divergence. An optical collimationsystem, shown in FIG. 4 by the lens C, provides for collimating thelaser beam B, directing it to an optical focusing system arrangeddownstream, represented by the lens F, capable of producing a focusedlaser beam. At first approximation, an ideal laser beam, i.e. a laserbeam ideally collimated in parallel rays, downstream of an opticalfocusing system is concentrated on a focal point according to the lawsof geometric optics. Physical laws of diffraction, however, indicatethat the laser beam even in the best collimation and focusingconfiguration has, downstream of the optical focusing system, a finitefocal spot at its waist. This is represented in FIG. 4 by the regionindicated W, which corresponds to the focal area of the beam B.Generally, in industrial processing uses, the working plane of amaterial coincides with the transversal plane at the waist of the beam.

FIG. 5 shows the distribution of the power density of a normallycollimated laser beam, which is typically Gaussian in shape withrotational symmetry in the case of a single-mode beam, i.e. with powerconcentrated around the longitudinal axis of the beam (Z axis) andgradually decreasing along a peripheral skirt, or it may be described asthe envelope of Gaussian profiles with rotational symmetry in the caseof a multi-mode beam.

The use of beams with a single-mode or multi-mode laser radiation, whichmay be described in a first approximation as Gaussian, meetstechnological control requirements in the field of high-power laserapplications. Indeed, a Gaussian beam is easily described by a fewparameters and is easily controllable in its propagation along anoptical transport path from an emitting source to the head of aprocessing machine because it has the characteristic of propagatingitself without modifying the power distribution, whereby it may bedescribed via a radius value and a divergence value in far-fieldpropagation conditions (in which case a geometric optics approximationmay be used). In the propagation conditions of the focused beam in thenear-field along a working path where the geometric optics approximationis no longer valid, the beam in any case maintains the Gaussian powerdistribution pattern in each of its cross sections.

For these reasons, in the field of laser processing, there has alwaysbeen a need to control the propagation of the laser beam so that it hasa Gaussian (or approximately Gaussian) cross-sectional powerdistribution and to establish once and for all the relative mutualposition between the optical axis of propagation of the laser beam andthe barycentric axis of the assist gas flow.

A number of solutions have been developed in the prior art adapted toprovide a stability (if not a rigidity) of positioning between theoptical axis of propagation of the laser beam and the outflow axis ofthe assist gas, and this generally involves the coincidence of the twoaxes. The adjustment of the mutual position between the optical axis ofpropagation of the laser beam and the axis of the assist gas flow isperformed in the prior art by means of a mechanical centering procedureperformed manually by an operator during periodic calibration of themachine (working head), for example when it is necessary to change thenozzle due to wear. Such a mechanical centering procedure involves aplurality of fine mechanical adjustments, for example by means of ascrew drive on the deflector mirror or on the collimation or focusinglenses to adjust the inclination and centering of the opticalpropagation system of the laser beam relative to the positioning of thenozzle on the head.

This design choice, which in the case of a purely single-mode beamrespects the rotational symmetry of the beam and the assist gas flow,respectively dictated by the Gaussian distribution of the power of thelaser beam and by the circular section of the mouth of the outflownozzle of the assist gas, ensures the isotropy of the behavior of eachworking process (cutting, welding, etc.) with respect to the directionsthat processing may follow.

The isotropy of the process with respect to the working paths on thematerial has always been considered advantageous where a laser workingprocess is controlled by electronic processing means according to anypaths and geometries, predetermined in CAD/CAM systems.

SUMMARY OF THE INVENTION

It is widely believed that a physically “unbalanced” system or withoutrotational symmetry at the points of incidence of the laser beam and theassist gas on the material results in complexity and difficulties incontrolling the working paths, or worse quality of the processingresults.

The object of the present invention is to provide a laser processingmethod with improved performance in terms of the operating speed,quality of results and cost-effectiveness of the process.

Another object of the present invention is to provide a laser processingmethod controllable in real time to obtain precise processing results inall operating conditions, achievable without increasing the size ofexisting machines.

According to the present invention, these objects are achieved via alaser processing method of a metallic material having the featuresreferred to in claim 1.

Particular embodiments are object of the dependent claims the content ofwhich is to be understood as an integral part of the presentdescription.

A further object of the invention is a machine for the laser processingof a metallic material and a computer program, as claimed.

In summary, the present invention builds on the consideration that abreaking of the rotational symmetry of the laser beam and assist gasflow assembly, i.e. a departure from the condition of coincidencebetween the propagation axes of the laser radiation and the outflow axisof the assist gas flow, may allow one to obtain better benefits in termsof speed, quality and cost-effectiveness than the working process withthe same performance.

The modes of application and exploitation of the breaking of rotationalsymmetry may be different, and in particular such modes comprise a“static” modification of the position of the optical axis of theprocessing laser beam relative to the axis of symmetry of the assist gasflow and a “dynamic” modification or in an “apparent beam” regime of theposition of the optical axis of the processing laser beam relative tothe axis of symmetry of the assist gas flow.

In the case of “static” modification, the relative position of theoptical axis of the laser beam relative to the axis of symmetry of theassist gas flow (distance, angle relative to a local advance directionalong the working path, assumed as reference direction) is fixed orvaried at a comparable relative speed (i.e., of the same order ofmagnitude) with the advance speed of the working process.

As a result of an imbalance of the position of the optical axis of thelaser beam, ahead of the axis of symmetry of the assist gas flow in thetranslation direction of the aforementioned gas flow (i.e. the area ofincidence of the axis of symmetry of the gas flow on the surface of thematerial being processed in the case of a cutting process), a betterperformance in terms of process speed may be obtained. Such imbalanceindeed generates a molten groove area hit by the assist gas flow whichis greater than the symmetrical case of coincidence of the axes. Inother words, the incidence of the laser beam on the material in advanceof the gas flow allows a lower pressure gas delivery at the same speedcompared to the symmetrical case of coincidence of the axes, ensuring alower gas consumption proportional to the lower pressure.

In the case of “dynamic” modification or “apparent beam” regime, therelative position of the optical axis of the laser beam relative to theaxis of symmetry of the assist gas flow (distance, angle relative to alocal advance direction along the working path, taken as a referencedirection) is varied at a relative speed of at least one order ofmagnitude greater than the advance speed of the working process. Theoptical axis of the laser beam is controlled in a periodic movementrelative to the axis of the flow of the assist gas at a predeterminedsurrounding movement frequency, in order to make sure the workingprocess on the material sees an apparent beam describable by theenvelope of the beam's movement at a frequency scale on an order ofmagnitude less than the surrounding movement frequency.

As a result of an oscillating, back and forth movement of the opticalaxis relative to the propagation direction of the axis of the assist gasflow, an apparent beam with a somewhat elongated elliptical shape is forexample determined, which allows a greater illumination of the moltengroove, i.e. an illumination that lasts longer in the groove, which inturn allows greater absorption of the radiation by the material in thedirection of propagation. This technique allows an electric powersavings, because it increases the yield per watt of power of the laserbeam, and conserves gas, because it keeps the material in a less viscouscondition than the prior art, whereby it is possible to push the moltenmaterial out of the groove with less gas pressure.

Otherwise, as a consequence of a circular oscillation movement of theoptical axis, i.e. the barycenter of distribution of the laser power,around the axis of the assist gas flow a circular apparent beam isdetermined, for example, which allows the diameter (apparent) of thelaser beam power distribution to increase, and thus a greater gas flowwithin the groove is obtained at the same pressure.

According to the invention, the application of the aforementionedconsiderations to the systems of the prior art is achieved byimplementing an efficient control of the position of the optical axis ofthe processing laser beam relative to the axis of symmetry of the assistgas flow by means of controlling the shape of the laser beam in realtime, i.e. by means of a modification of the transverse powerdistribution of the beam, which substantially preserves the shape andthe effective diameter of the beam.

The present invention is based on the principle of using an opticalsystem with controlled deformation known per se in scientificapplications for the processing of optical signals (hence of low-poweroptical radiation) to shape a high-power laser beam for industrialapplications.

The application of a controlled deformation optical system in a laserbeam optical transport system allows the range of shaping of the laserbeam obtainable in a rapidly modifiable manner to be expanded and toregulate with extreme precision the mutual position between thepropagation axis of the laser radiation and the outflow axis of theassist gas, and consequently to improve performance in the machiningprocesses or to implement innovative machining processes.

Advantageously, the method of the invention allows the laser beam to bedirected at the center of the assist gas outflow region with highprecision, thus preventing the need for precise mechanical adjustmentsby means of an operator's intervention when setting the machine for apredetermined process.

Still more advantageously, the method of the invention allows theposition of the optical axis of the laser beam to be controlledaccording to a predetermined spatial relationship to the axis of theassist gas flow, which is not necessarily a coaxially aligned position,with a quick adjustment time so that such position control may not onlybe performed as a “preparatory setup” for a processing cycle but mayalso be implemented in real time during a working process in such a wayas to control the desired mutual position between the optical axis ofthe laser beam and the axis of the assist gas flow along the workingpath on the material.

In other words, the method of the invention allows a predeterminedmutual positioning strategy to be automatically set and maintainedbetween the optical axis of the laser beam and the axis of the assistgas flow during a working process, e.g. by instantaneously controllingthe position of the optical axis of the laser beam at a predetermineddistance from the axis of the assist gas flow and at a predeterminedangular direction relative to the current direction of the working path(the advance direction of the process).

The method of the invention further allows a mutual positioning variablestrategy between the optical axis of the laser beam and the axis of theassist gas flow to be set automatically during a working process, e.g.as a function of the spatial position of the working area on thematerial along a predetermined working path or as a function of otherparameters, such as the variations in advancing speed along the workingpath, the thickness variations of the working material, the variationsof the angle of incidence of the assist gas relative to the surface ofthe material being processed.

Variations in the advancing speed along the working path arise from thenecessary stops of the various mechanical control axes of the workinghead that contribute to the definition of the path itself, e.g. due tothe reversal of the working direction or orientation of the head, whichis preceded by a slowdown until stopping and is followed by a subsequentacceleration, both in the case of a cutting and of a welding process.

Changes in the thickness of the working material, known and expected,require not only a corresponding advancing speed and focal spot positionwithin the material itself that are different depending on thethickness, but may also require a different mode for breaking therotational symmetry, i.e. a “static” or “dynamic” modification of theposition of the optical axis of the processing laser beam relative tothe axis of symmetry of the assist gas flow as a function of saidthickness.

Finally, variations in the angle of incidence of the assist gas relativeto the surface of the working material require a different distributionof laser power around the axis of the gas flow to improve the cuttingperformance, ensuring a more stable process due e.g., to a wider grooveor to a better delivery of the assist gas supply.

The control of the mutual position between the propagation axis of thelaser radiation and the assist gas outflow axis is implemented accordingto the invention by means of a control of the transverse powerdistribution of the beam in an area of the working plane on the metallicmaterial in a predetermined neighborhood of the assist gas flow axisdefining a delivering area of said flow. The delivering area of theassist gas flow—which represents the volumetric field of action of thecontrol method of the invention—is identifiable as the “affected volume”of the nozzle of a working head—a nozzle typically having a mouth whosediameter is between 1 mm and 3.5 mm and dimensions which are typical ofa truncated cone with a height of 6 mm to 20 mm, a smaller base (at thenozzle) of diameter equal to the mouth diameter increased by 1 to 3 mm,and a larger base whose characteristic dimension is a function of theheight of the frustoconical volume and the angle of inclination of thegenerating line, typically between 15 and 30 degrees. Appropriately, thevolume of the nozzle is as small as possible, and it has the slimmestappearance possible so that it may also operate within concavities ofthe surfaces to be processed.

Advantageously, the automatic control performed by the method of theinvention may be carried out in real time with operating frequenciesbetween 100 Hz and 10 kHz.

A control system adapted to carry out the method of the invention isadvantageously distinguished from the prior art systems because it maybe integrated into a working head, i.e. it is independent from thegeneration of the laser beam and from its conveyance to the workinghead.

Moreover, unlike the known solutions for setting or commissioning amachine for a specific process, wherein the position of the optical beamrelative to the assist gas flow is adjustable as a result of a manualintervention by an operator, or wherein the modification of thedirection of incidence of the optical beam is implemented according to apredetermined logic, as is the case in the prior art of wobbling, bymeans of which a high dynamic oscillation, programmed when setting aworking program, is repeatedly imparted to the optical axis ofpropagation of the laser beam throughout the entire process, the methodof the invention allows the position of the optical axis of propagationof the laser beam to be effectively controlled in real time as afunction of the beam's location along a working path, whereby it ispossible to change the mutual position between the optical propagationaxis of the optical beam and the axis of the assist gas flow on a timelybasis depending on the programmed working conditions that occur atpredetermined positions along the working path. Such programmed workingconditions include, by way of illustrative and non-limiting example, thecurrent working position (or, more generally, the area of the currentworking plane) along a predetermined working path and/or the currentdirection of the working path on the material and/or the translationdirection of the axis of the assist gas flow.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will be described ingreater detail in the following detailed description of one embodimentthereof, given by way of non-limiting example, with reference to theaccompanying drawings wherein:

FIGS. 1 and 2 are examples of machines for laser processing according tothe prior art;

FIG. 3 shows an example of the structure of a working head of a lasermachine according to the prior art;

FIGS. 4 and 5 show a schematic representation of the shape of a laserbeam for applications of industrial processing of metallic materialsaccording to the prior art;

FIG. 6 is a schematic diagram of an optical path of a laser beam in aworking head adapted to perform the method of the invention;

FIG. 7 is a schematic representation of a controlled surface reflectingelement for the shaping of the optical beam for the implementation ofthe method of the invention;

FIG. 8 is a block diagram of control electronics of a laser processingmachine, adapted to perform a processing method according to theinvention; and

FIG. 9 is a schematic representation of a working example according tothe method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 through 5 have been previously described with reference to theprior art and their contents are hereby referred to as being common tothe manufacture of a processing machine controlled for carrying out aworking process according to the teachings of the present invention.

An optical path of a laser beam in the working head of a machine for thelaser processing of metallic materials according to the invention isdiagrammed in FIG. 6.

The optical system of FIG. 6 comprises an input device 100 of a laserbeam B, such as e.g. the end of a fiber optic cable or an optical pickupsystem of a beam propagated by an emitting source along an optical pathin free space, from which the laser beam B emerges with a predetermineddivergence.

Downstream of the input device 100, an optical collimation system 120 isarranged, for example a collimation lens (typically a collimation lensfor a working head of a laser cutting machine has a focal length from 50mm to 150 mm), downstream of which the collimated laser beam isconducted to an optical focusing system 140, e.g. a focusing lens(typically a focusing lens for a working head of a laser cutting machinehas a focal length from 100 mm to 250 mm), arranged to focus the beam ona working plane Π through a screen or protective glass 160.

In the optical path between the collimation optical system 120 and theoptical focusing system 140, optical beam shaping means 180 areinterposed.

In particular, with reference to the schematization of the optical pathof a laser beam shown in FIG. 6, the present invention relates to makingoptical means 180 for shaping the laser beam and the control of saidmeans for achieving a transverse power distribution of the laser beam ina controlled manner on a predetermined working plane of the material. Inthe figure, the optical means 180 for shaping the laser beam are shownin an illustrative embodiment wherein they are arranged with their ownaxis of symmetry at 45° relative to the propagation direction of thebeam.

To this end, the optical means 180 for shaping the laser beam are madeas a deformable reflecting element 200 with a controlled surface,comprising a plurality of reflection areas independently movable, asdiagrammed in FIG. 7, which, in a rest state, define a reflectivesurface lying on a reference reflection plane. Said deformable,controlled surface reflecting element 200 provides a continuous foilmirror, the reflective surface of which is modifiablethree-dimensionally with respect to the reference flat reflectivesurface adopted in the rest state. Said deformable, controlled surfacereflecting element 200 has a reflective surface with continuouscurvature including a plurality of reflection areas with which there isassociated posteriorly a corresponding plurality of movement modulesshown in the figure with 200 a, 200 b, . . . and is appropriatelytreated for the use with high optical power by virtue of the joint useof a highly reflective coating (at least 99%) at the wavelength of thelaser beam, and a mounting on a contact holder, cooled with water bydirect channeling. The movement modules are integral to the continuouscurvature reflective surface and are independently movable. Thereflection areas of the reflective surface with continuous curvaturehave no edges between them, i.e., the overall reflective surface hascontinuous local derivatives in all directions. The movement of saidplurality of movement modules 200 a, 200 b includes translationmovements of the corresponding reflection areas, such as forward orbackward movements, relative to the reference flat reflective surfaceadopted in the rest state or rotational movements of the correspondingreflection areas around an axis parallel to the reference flatreflective surface adopted in the rest state, or even a combination ofthe same. The deformations of the reflecting surface, i.e. the movementsof the movement modules 200 a, 200 b, are preferably actuated by knownpiezoelectric techniques, which make it possible to control the movementof the movement modules and the consequent position of the reflectionareas, i.e. their modification of position resulting from a combinationof movement by translation and/or rotation of each module at apredetermined number of degrees of freedom independently of the others,typically on travels on the order of +/−40 μm, by means of which it ispossible to obtain approximations of continuous curvature surfacesdefined by combinations of Zernike polynomials, through which it ispossible (at least in theory and with sufficient approximation inpractice for the desired purposes) to apply an adjustment of theposition of the optical propagation axis of the laser beam or moregenerally a control of the transverse power distribution of the laserbeam, according to the objects of the desired processing applications.

FIG. 7 shows a preferred embodiment of the reflector element 200 with anelliptical profile and the related rear movement modules, adopted for anangle of incidence of the collimated laser beam of 45°, as shown in thediagram of FIG. 6. Such embodiment is to be understood as purelyillustrative and non-limiting to the implementation of the invention. Ina different preferred embodiment, wherein the incidence of thecollimated laser beam is perpendicular or almost perpendicular to thesurface of the element 200 in the rest state, the profile of thereflective element 200 is a circular profile.

In the embodiment of the reflective element with an elliptical profile,the same has a major axis of 38 mm and a minor axis of 27 mm,corresponding to the maximum transverse aperture size of the laser beamincident on the mirror obtainable by the collimation optical system 120.

Specifically, in a preferred embodiment, said deformable, controlledsurface reflecting element 200 includes a plurality of reflection areasindependently movable by means of a corresponding plurality of movementmodules which comprise a central area and a plurality of ranks ofcircular crown sectors concentric to said central area. In the currentlypreferred embodiment, the ranks of concentric circular crown sectors are6 in number, the circular crown sectors are 8 in number for each rank,and the height of the circular crown sectors increases from the first tothe third rank and from the fourth to the sixth rank in the radialdirection to the outside of the reflective element. The height of thecircular crown sectors of the fourth rank is intermediate between theheight of the circular crown sectors of the first and second rank.Preferably, in order to simplify the control structure of the reflectingelement 200 as designed, the plurality of circular sectors forming theperipheral circular crown may be fixed, and only the ranks of the innercircular crown sectors are movable in such a way that they may employ atotal number of actuators limited to 41.

In general, the numbers of ranks of circular sectors, the number ofcircular crown sectors and the height of the circular crown sectors aredetermined according to the reflecting surface geometries necessary forobtaining predetermined desirable transverse power distributions of thelaser beam, through simulation procedures of the trends of thetransverse power distributions of a laser beam incident on thereflective element for a selected number of reflection areas. In fact,the controlled deformability of the reflection surface of the element200 induces controlled variations of the intensity of the laser beam onthe focal plane by acting on the phase of the laser beam. In thecurrently preferred embodiment, the deformation of the surface of thereflective element 200 is controlled in such a way as to determine areflective surface ascribable to a combination of Zernike polynomials.Thus, the distribution of the intensity of the laser beam on the focalplane according to the phase variations controlled by the movement ofthe reflection areas of the reflective element 200 may be advantageouslysimulated using mathematical calculation methods.

The geometry of the subdivision of the surface of the reflecting element200 illustrated in FIG. 7—corresponding to the geometry of the movementmodules of the reflection areas—has been determined by the inventorsthrough a simulation procedure to obtain different forms of transversepower distribution with a great freedom in beam shaping, even notrelated to the retention of the rotational symmetry thereof. Otherwise,for applications strictly related to the Gaussian power distribution,wherein a change in the shape of the power distribution is not required,but only the displacement thereof with respect to the opticalpropagation axis, it is possible to use simpler geometries, for exampleequally spaced ranks, i.e. wherein the height of the circular crownsectors is constant among all the ranks of the sectors. For applicationswherein a rotational symmetry of the beam power distribution is to beretained, it is possible to provide for a plurality of reflection areasand respective movement modules in the form of radially independentcircular crowns.

FIG. 8 shows a circuit diagram of an electronic control system of amachine for the laser processing of metallic materials for theimplementation of the method of the invention.

The system comprises electronic processing and control means shown inthe figure collectively at ECU, which may be integrated into a singleprocessing unit on board a machine or implemented in a distributed form,thus comprising processing modules arranged in different parts of themachine, including, for example, the working head.

Memory means M associated with the electronic processing and controlmeans ECU store a predetermined processing pattern or program, forexample comprising a predetermined working path in the form of movementinstructions for the working head and/or for the material beingprocessed, and physical processing parameters indicating the powerdistribution of the optical beam, the power intensity of the beam, andlaser beam activation times as a function of the working path.

The electronic processing and control means ECU are arranged foraccessing the memory means M to acquire a working path and to controlthe application of the processing laser beam along said path. Thecontrol of the application of the laser beam along the predeterminedworking path includes the control of the delivery of an assist gas flowand the control of the radiation of a predetermined power distributionof the laser beam toward a predetermined working area by reference tothe predetermined processing pattern or program, i.e., according to theworking path information and working parameters acquired from the memorymeans.

The sensor means SENS are arranged on board the machine to detect inreal time the mutual position between the working head and the materialbeing processed as well as the change over time of such position.

The electronic processing and control means ECU are arranged to receivefrom the sensor means SENS signals indicative of the mutual positionbetween the working head and the material being processed over time,i.e. the change of the area of the current working plane and/or of thecurrent direction of the working path over time.

The electronic processing and control means ECU comprise a first controlmodule CM1 for controlling the mechanical parameters of the processing,arranged to emit first command signals CMD₁ to a known assembly ofactuator means, comprising actuator means for moving the working headalong the degrees of freedom allowed to it by the specific embodiment ofthe machine and actuator means for moving the material being processedwith respect to the position of the working head, adapted to cooperatewith the actuator means for moving the working head to present aprogrammed working path on the material being processed at the nozzle ofthe working head. These actuator means are not described in detailbecause they are known in the art.

The electronic processing and control means ECU comprise a secondcontrol module CM2 for controlling the physical parameters of theprocessing, arranged to emit second command signals CMD₂ to assist gasflow delivery means and control means for generating and transmittingthe laser beam.

The electronic processing and control means ECU comprise a third controlmodule CM3 for controlling the optical processing parameters, arrangedto emit third command signals CMD₃ to the deformable, controlled surfacereflecting element 200 of the optical beam shaping means for theimplementation of the movement modules of the independently movablereflection areas of said element, i.e. to control their mutual spatialdisplacement (translation along the optical axis of the reflectingelement or inclination relative to it). The command signals CMD₃ areprocessed by means of a computer program comprising one or more codemodules having instructions of a regulation model or program for theimplementation of the method of the invention according to thepredetermined shaping of the laser beam to be obtained, i.e. toestablish a predetermined transverse power distribution of the laserbeam, and consequently a predetermined position of the opticalpropagation axis of the laser beam, as a function of the instantaneousprocessing conditions along an optical propagation axis incident on thematerial in an area of at least one working plane of the metallicmaterial, the working plane of the material being the surface plane ofthe material or a plane which varies in depth in the thickness of thematerial, e.g. for cutting or drilling of thick materials, i.e.typically with thicknesses greater than 1.5 times the Rayleigh length ofthe focused beam (in the typical case, thicknesses greater than 4 mm andup to 30 mm). The aforementioned command signals CMD₃ are also processedby the computer program to establish the predetermined transverse powerdistribution of the laser beam in a predetermined neighborhood of theaxis of the assist gas flow and within a delivering area of said flowaccording to the instantaneous working conditions, i.e., the area of thecurrent working plane and/or the current direction of the working pathon the metallic material.

The electronic processing and control means ECU are therefore arrangedto detect the current position and/or the current translation directionof the axis of the assist gas flow to control the relative translationof the axis of the assist gas flow along a predetermined working path onthe metallic material and to automatically adjust the position of theoptical propagation axis of the laser beam or the transverse powerdistribution of the laser beam according to the current position and/orthe detected current direction of translation of the axis of the assistgas flow.

The position of the optical propagation axis of the laser beam isgoverned by controlling the movement modules of the reflection areas soas to carry out predetermined general inclination movements of thereflecting element as a whole relative to the respective rest statewhich determine the spatial translation of the spot of the laser beam onthe material being processed.

According to one embodiment, the position of the optical propagationaxis of the laser beam is adjusted so as to be selectively oralternately in a front area and in a rear area with respect to thecurrent position of the axis of the assist gas flow along the workingpath during a cutting operation of the metallic material. This ispreferably done in the pursuit of a cutting path, for example as afunction of the speed of execution of the cutting operation and thethickness of the material to be cut.

In the case of a “static” modification, as a result of an imbalance ofthe position of the optical axis of the laser beam ahead of the axis ofsymmetry of the assist gas flow in the direction of translation of theaforementioned gas flow (i.e., of the area of incidence of the axis ofsymmetry of the gas flow on the surface of the material being processedin the case of a cutting process) a better performance in terms ofprocess speed may be obtained. Such imbalance generates a molten groovearea hit by the assist gas flow, which is greater than the symmetricalcase of coincidence of the axes. In other words, the incidence of thelaser beam on the material ahead the gas flow allows a lower pressuregas delivery at the same speed compared with the symmetrical case ofcoincidence of the axes, ensuring a lower gas consumption proportionalto the lower pressure.

In the case of “dynamic” modification or “apparent beam” regime, as aresult of an oscillation movement of the optical axis back and forthrelative to the direction of propagation of the axis of the assist gasflow, for example an apparent beam with an elongated quasi-ellipticalshape is determined, which allows for better illumination of the moltengroove, i.e., an illumination that lasts longer on the groove, which inturn allows greater absorption of radiation by the material in thedirection of propagation. This technique allows an electrical powersavings, because it increases the yield per watt of power of the laserbeam, as well as a gas savings, because it keeps the material in a lessviscous condition compared with the prior art, whereby it is possible topush the molten material out of the groove with less gas pressure.

In another embodiment, the position of the optical axis of propagationof the laser beam is adjusted so as to follow a circular path around thecurrent position of the axis of the assist gas flow during a drillingoperation of the metallic material. This allows an “apparent beam” withwide diameter circular symmetry to be generated, even if starting with aGaussian beam of a smaller diameter, with two advantages. The firstadvantage is that the drilling diameter is increased at the end of theprocess, and thus allows, in the delicate phase at the beginning of thecutting movement, a better coupling between the laser beam and theadvancing front within the thickness of the material being processed, aswell as a greater gas flow, which allows a more efficient expulsion ofthe molten material at the start. The second advantage is that duringthe drilling process, the circular movement imparts a preferentialdirection of emission on the molten material, which must necessarilyexit from the surface of the material processing area from the sidewherein the drilling occurs, facilitating the progressive denudationefficiency of ever deeper layers of material, and, ultimately, a fasterbreakdown of the overall thickness.

FIG. 9 shows an example of processing according to the method of thepresent invention.

In the figure, a programmed working path is indicated at T. The workingpath includes a cutting profile comprising, by way of example, a seriesof curved sections T1, T2 or straight sections T3, forming a closed oropen broken line, and a series of recesses, e.g. recesses with asemi-circular profile R1, R2. The working path T also includes acircular drilling profile, indicated at H, at a predetermined distancefrom the cutting profile.

At some illustrative positions of the working head along theaforementioned path (the working head is diagrammed only in associationwith an initial working position, in order to not overly complicate thegraphic representation), the delivering areas of the assist gas flow onthe material being processed are indicated at G1, . . . , Gn, and thespots of incidence of the laser beam on the material being processedcircumscribed around the positions of the optical axis of the laser beamare indicated at S1, . . . , Sn. It should be noted that, typically, forcutting and/or drilling operations on carbon steel with thicknesses from4 mm to 30 mm, stainless steel with thicknesses from 4 mm to 25 mm,aluminum alloys with thicknesses from 4 mm to 15 mm, copper and brasswith thicknesses from 4 mm to 12 mm, the typical size of the deliveringarea of the assist gas flow ranges from 1.8 mm to 3 mm, and the spot ofincidence of the laser beam ranges from 0.05 mm to 0.25 mm

For some working positions or areas along the working path, there arerepresented, by way of example, the corresponding delivering area of theassist gas flow on the material being processed (circular, in the mostcommon embodiment of a circular nozzle) and one or more spots ofincidence of the laser beam (which are also represented by way ofillustration by a circular shape, in the common case of transverse powerdistribution of a Gaussian shape).

G1 indicates a first delivering zone of the assist gas flow in a laserbeam advancing section along a first segment T1 of a cutting linefollowing a predetermined path T. In this working area, the position ofthe optical axis of propagation (of the power distribution) of the laserbeam is adjusted so that the spot S1 of incidence of the beam on theworking plane lies in a zone ahead of the current position of the axisof the assist gas flow, which corresponds to the barycenter of the G1zone.

G2 indicates a second delivering zone of the assist gas flow in anadvancing section of the laser beam in deceleration along the segment T1of the cutting line of the path T. In this working area, the position ofthe optical propagation axis (of the power distribution) of the laserbeam is adjusted so that the spot S2 of incidence of the beam on theworking plane is substantially coincident with the current position ofthe axis of the assist gas flow, corresponding to the barycenter of theG2 zone.

G3 indicates a third delivering area of the assist gas flow at thesemi-circular recess R1 of the path T. In this working area, theposition of the optical propagation axis (of the power distribution) ofthe laser beam is adjusted in a way such that the spot of incidence ofthe beam on the working plane travels the desired cutting path withinthe delivering area of the assist gas flow without the movement of theaforementioned zone, as indicated by the subsequent positions S3, S4, S5and S6, radially equidistant from the current position of the axis ofthe assist gas flow, which corresponds to the barycenter of the G3 zone,but angularly offset from a rearward position to a forward positionrelative to the current direction of the working path on the metallicmaterial.

G4 indicates a fourth delivering area of the assist gas flow at avariation of direction between the section T2 and the section T3 of thecutting profile, wherein the variation of direction has a small radiusof curvature. In this working area, the position of the optical axis ofpropagation (of the power distribution) of the laser beam is adjusted sothat the spot of incidence of the beam on the working plane travels thedesired cutting path within the delivering area of the assist gas flow,without movement of the aforementioned zone, as indicated by thesubsequent positions S7, S8, and S9, having a radial distance and anangular position different from the current position of the axis of theassist gas flow, which corresponds to the barycenter of the G4 zone,i.e. respectively rearward, coincident and forward positions relative tothe current direction of the working path on the metallic material.

Finally, G5 indicates a fifth delivering area of the assist gas flow atthe circular drilling profile H which can be reached at a predetermineddistance from the path T of the cutting profile, by interrupting thelaser beam emission for a predetermined time. In this working area, theposition of the optical propagation axis (of the power distribution) ofthe laser beam is adjusted so that the spot of incidence of the beam onthe working plane travels a circular path within the delivering area ofthe assist gas flow, possibly coaxial to the axis of the assist gasflow, which corresponds to the barycenter of the G5 zone, withoutmovement of the aforementioned zone, which is indicated by thesubsequent positions S10, S11, S12 and S13.

Naturally, without altering the principle of the invention, theembodiments and the details of implementation may vary widely withrespect to that which is described and illustrated purely by way ofnon-limiting example, without thereby departing from the scope ofprotection of the invention defined by the appended claims.

What is claimed is:
 1. A method of laser processing of a metallicmaterial, in particular for laser cutting, drilling or welding of saidmaterial, by means of a focused laser beam having a predeterminedtransverse power distribution on at least one working plane of themetallic material, comprising the steps of: providing a laser beamemitting source; leading the laser beam emitted by said emitting sourcealong a beam transport optical path to a working head arranged inproximity to said metallic material; collimating the laser beam along anoptical axis of propagation incident on the metallic material; focusingsaid collimated laser beam in an area of a working plane of saidmetallic material; and conducting said focused laser beam along aworking path on the metallic material comprising a succession of workingareas, wherein the method comprises shaping the laser beam, whereinshaping the laser beam comprises: reflecting said collimated beam bymeans of a deformable controlled surface reflecting element having areflecting surface with a continuous curvature including a plurality ofindependently movable reflection areas, and controlling the arrangementof said reflection areas to establish a predetermined transverse powerdistribution of the beam on at least one working plane of the metallicmaterial as a function of the area of the current working plane and/orthe current direction of the working path on the metallic material. 2.The method according to claim 1, comprising the steps of: delivering aflow of assist gas towards said area of the working plane of themetallic material along an axis of the assist gas flow, and controllingthe arrangement of said reflection areas to establish said predeterminedtransverse power distribution of the beam in an area of the workingplane on the metallic material comprised in a predetermined neighborhoodaround the axis of the assist gas flow and within a delivering area ofsaid flow.
 3. The method according to claim 1, wherein controlling thearrangement of said reflection areas of the controlled surfacereflecting element comprises controlling a combination of moves of saidareas with respect to a reflecting reference flat surface.
 4. The methodaccording to claim 3, wherein controlling a combination of moves of saidreflection areas of the controlled surface reflecting element comprisescontrolling the translation movement of said areas along the opticalaxis of the reflecting element and/or the rotation of said areas toobtain an inclination with respect to the optical axis of the reflectingelement.
 5. The method according to claim 2, comprising the relativetranslation of the axis of the assist gas flow along a predeterminedworking path on the metallic material, the detection of the currentposition and/or of the direction of the current translation of the axisof the assist gas flow, and the automatic adjustment of the position ofthe optical axis of propagation of the laser beam as a function of thedetected current position and/or of the detected current translationdirection of the axis of the assist gas flow.
 6. The method according toclaim 2, comprising the relative translation of the axis of the assistgas flow along a predetermined working path on the metallic material,the detection of the current position and/or the detection of thecurrent direction of translation of the axis of the assist gas flow, andthe automatic control of the transverse power distribution of the laserbeam as a function of the detected current position and/or of thedetected current direction of translation of the axis of the assist gasflow.
 7. The method according to claim 5, wherein the automaticadjustment of the position of the optical axis of propagation of thelaser beam as a function of the detected current position and/or of thedetected current direction of translation of the axis of the assist gasflow is performed by reference to a predetermined adjustment pattern orprogram.
 8. The method according to claim 6, wherein the automaticcontrol of the transverse power distribution of the laser beam as afunction of the detected current position and/or of the detected currentdirection of translation of the axis of the assist gas flow is performedby reference to a predetermined adjustment pattern or program.
 9. Themethod according to claim 5, wherein the position of the optical axis ofpropagation of the laser beam is adjusted so as to be alternately in afront area and in a rear area with respect to the current position ofthe axis of the assist gas flow along the working path during a cuttingoperation of the metallic material.
 10. The method according to claim 5,wherein the position of the optical axis of propagation of the laserbeam is adjusted so as to follow a circular path around the currentposition of the axis of the assist gas flow during a drilling operationof the metallic material.
 11. The method according to claim 1,comprising providing a deformable controlled surface reflecting elementhaving a reflecting surface with a continuous curvature including aplurality of independently movable reflection areas by means of acorresponding plurality of movement modules which include a central areaand a plurality of ranks of circular crown sectors concentric to saidcentral area.
 12. The method according to claim 11, wherein said ranksof concentric circular crown sectors are in number of 6, the circularcrown sectors are in number of 8 for each rank, and the height of thecircular crown sectors is increasing from the first to the third rankand from the fourth to the sixth rank in the radial direction towardsthe outside of the reflecting element, the height of the circular crownsectors of the fourth rank being intermediate between the height of thecircular crown sectors of the first and second rank.
 13. A machine forlaser processing of a metallic material, in particular for lasercutting, drilling or welding of said material, by means of a focusedlaser beam having a predetermined transverse power distribution on atleast one working plane of the metallic material, comprising: a laserbeam emitting source; means for leading the laser beam emitted by saidemitting source along a beam transport optical path to a working headarranged in proximity of said metallic material; optical means forcollimating the laser beam along an optical axis of propagation incidenton the metallic material; optical means for focusing said collimatedlaser beam in an area of a working plane of said metallic material,wherein at least said focusing optical means of said collimated laserbeam are carried by said working head at a controlled distance from saidmetallic material; and means for adjusting the distance between saidworking head and said metallic material, adapted to conduct said focusedlaser beam along a working path on the metallic material comprising asuccession of working areas, optical means for shaping the laser beamincluding a deformable controlled surface reflecting element having areflecting surface with a continuous curvature including a plurality ofindependently movable reflection areas, adapted to reflect saidcollimated laser beam, the arrangement of said reflection areas beingadapted to establish a predetermined transverse power distribution ofthe beam on at least one working plane of the metallic material; andelectronic processing and control means arranged to implement a shapingof said laser beam in accordance with the method of laser processingaccording to claim
 1. 14. A computer program comprising one or more codemodules for performing a method of shaping a laser beam in a machine forlaser processing of a metallic material, in accordance with the methodof laser processing according to claim 1, when the program is executedby electronic processing and control means of said machine.